When feeding livestock for market, it is the usual practise to keep them in agricultural buildings, barns and the like and feed them carefully controlled rations. In this way, the period of time required to bring them up to market weight is reduced, and labour requirements are minimized.
However, the presence of a large number of livestock in a confined space such as a barn creates problems of heating and cooling the interior of the barn, and of providing fresh air and good ventilation. If livestock do not have adequate fresh air they will become sickened. Similarly, if the temperature varies rapidly then will also suffer. In either case, losses will result either from sickness of death of animals, and further losses will result due to an increase in the time required to bring them up to market weight.
Various systems have been proposed for ventilating barns. Obviously, all such systems should remove a certain proportion of the air present in the barn, and introduce a certain proportion of fresh air into the barn which is then circulated throughout the space occupied by the livestock. It is not merely sufficient to introduce fresh air and to remove stale air. This may leave substantial pockets of stale or stagnant air which are not subject to circulation. Undoubtedly, a perfectly adequate circulation and ventilation could be obtained using modern sophisticated air conditioning techniques. However, the cost of such highly engineered air circulation systems is so great as to render them impractical for the purpose of ventilating a barn. It must particularly be borne in mind that the requirement for improved air circulation will frequently be at its greatest in existing buildings which may have been of inferior or older construction. Accordingly, any system, which is to be acceptable to the great majority of farmers and livestock breeders, must be economically priced, and effective in use both in summer and winter, and adaptable for installation in older buildings without any major modifications being required.
One of the more recent systems that have been proposed is disclosed in U.S. Letters Pat. No. 3,367,258, and a very similar system is proposed in U.S. Letters Pat. No. 3,363,531. In both of these systems, a single housing containing both a fresh air intake duct and a stale air exhaust duct is adapted to be mounted in the wall of a barn. A single fan operating in the exhaust duct draws air from the barn. The exhausing of air from the barn is intended to cause some fresh air to be drawn in through the intake duct. A double bladed damper may be moved so as to block off part of the air flowing out of the exhaust duct and redirect it into the intake duct. By varying the angle of the double bladed damper, more or less air may be redirected from the exhaust back into the intake duct. As more stale air is redirected from the exhaust and thus returned into the inlet duct, less fresh air is drawn into the into the inlet duct.
This system however suffers from a variety of disadvantages. In the first place, it does not provide for effective distribution of fresh air or recycled air into the interior of the barn. There will thus result a fairly rapid movement of air adjacent to the ventilator installation itself, and leaving a stagnant area of uncirculated air in the center of the barn. One of the results which has been frequently observed is that animals will then tend to stand as close as possible to the ventilator, leaving the other areas of the barn unoccupied. Animals in such close confinement may thus become subject to stress and injure each other. In addition, animal dung will accumulate in large quantities adjacent to the ventilator, and will have to be cleared away more frequently than would be the case if it were evenly distributed over the barn.
A further disadvantage is that the redirecting of air from the exhaust duct into the intake duct requires the air to change direction 180.degree.. This produces severe turbulance thereby greatly reducing the operating efficiency of the ventilator. When operating in the fully open condition ie., with the maximum air being exhausted and the maximum fresh air being drawn in, then an area of turbulance is likely to arise between the two air streams flowing in opposite directions at the exterior of the ventilator.
All of these factors make it difficult to achieve a precise adjustment between the incoming fresh air and the out going stale air so that fairly wide fluctuations in temperatures can take place as a result of only minor variations in the position of the two bladed damper, and the degree of control available is thus somewhat imprecise.